Example:You can test it by changing url of image.
<html>
<head>
</head>
<body>
<img src="a1.jpg" width="300px" onmouseover="this.width=500" onmouseout="this.width=300">
</body>
</html>
Do not change value of src in img tag of ur code.
Just add onmouseover and onmouseout to img tag like...